The present invention relates to a device for determining the presence and amount of an analyte via immunodiffusion assay techniques. The device features multiple binding zones and capillary channels to maintain uniform fluid flow. By these arrangements, the device allows detection of analyte concentration at multiple, pre-defined threshold levels. The invention also relates to a novel reservoir zone comprising a network of capillary channels. Methods for preparing the device and for determining the presence and amount of an analyte are also described herein.
Immunodiffusion techniques are found in a wide variety of applications including medical diagnosis. Generally, such techniques involve screening for the presence of an analyte by diffusing a solution suspected of containing the analyte through a solid support. Bound to the support is a binding agent which is a specific receptor for the analyte. An analyte contained in the sample eventually reacts with the immobilized binding agent. A reaction between the binding agent and analyte can be detected by a variety of indicators. For example, sandwich immunoassay techniques involve the formation of a three member complex of binding agent-analyte-label, and formation of the complex can be determined via visual, radioactive, spectroscopic, or other methods.
Immunodiffusion techniques can be useful in analyzing a large number of biological components, including antibodies, proteins, enzymes and nucleic acids, depending on the particular binding agents employed. For example, where the analyte is an antigen, typical binding agents are antibodies, and vice versa.
Many specific immunoassay methods have been reported.
U.S. Pat. No. 4,960,691 (Gordon et al.) describes a chromatographic test strip having a site for immobilizing an analyte. The site contains a reagent capable of reacting with the analyte and immobilizing it. Another diffusable reagent is bound upstream of this site that is capable of binding with the analyte-immobilized reagent couple. This other reagent may be a labeled material which can be detectable upon reaction with the couple.
U.S. Pat. No. 4,879,215 (Weng et al.) is directed to a method and device for determining the presence of an analyte and amounts of the analyte. Weng et al. describes the formation of a detectable signal which can relate to an amount of analyte present in the test solution. The detectable signal is formed by contacting a test strip having been traversed by a test solution with a developer solution containing components of a signal producing system. The detectable signal is compared to a control signal to determine an amount of the analyte.
U.S. Pat. No. 4,703,017 (Campbell et al.) is directed to a solid phase assay involving an antibody supported on a solid phase support. The antibody is capable of binding an analyte, typically a hapten or antigen. After contacting the solid support with a sample suspected of containing an analyte, any antibody that remains unbound by an analyte is contacted with a tracer. The bound tracer can be viewed visibly without the. aid of instrumentation. A test for hCG (pregnancy test) which is a simple yes/no at a single level of analyte is described.
U.S. Pat. No. 5,073,484 (Swanson et al.) is directed to a method and apparatus for quantitatively determining an amount of an analyte involving a liquid-permeable solid medium having a number of reaction zones. One embodiment of Swanson employs a filter paper strip having a series of reaction zones separated from each other by spacer layers. Swanson describes preparing the strip by binding a reactant to individual rectangular pieces of filter paper and alternately attaching these pieces with similar pieces of filter paper that do not contain a reactant. This results in portions of a fluid pathway which are discontinuous, due to an interface between one piece of filter paper and an adjacent piece of filter paper.
U.S. Pat. No. 5,756,362 (Durst et al.) discusses the use of capillary action to aid the assay process. The capillarity described therein is that inherent in microporous solid phase material which is known to be non-uniform in nature. To determine different concentration levels, a number of strips each having a measurement zone with a different concentration of a binding reagent is employed.
U.S. Pat. No. 5,458,852 (Buechler) details the difficulties of reliance on the capillarity of porous matrices in assay devices. Buechler discloses a non-porous medium which requires precision parts, aligned grooves and plasma treatment to graft functional groups to create hydrophilic surfaces for these devices. Such a requirement adds to the complexity and cost of manufacture of the assay device.
While many assay techniques exist, there remains a need to develop immunoassay techniques and products. If such techniques are to be used by the general public, ideally the methods should be user-friendly, and capable of being mass-produced in an inexpensive manner.
One aspect of the present invention provides a device for determining the presence of an analyte. The device comprises a layer including a continuous porous medium deposited thereon and a fluid pathway as defined by fluid barriers in the porous medium. At least a portion of the barriers define a capillary channel. The device also comprises an analysis zone within the fluid pathway comprising a plurality of binding zones for binding and immobilizing the analyte. Each binding zone is defined by a concentration of a binding reagent immobilized on the medium.
Another aspect of the invention provides a method for determining the presence of an analyte. The method involves applying a sample suspected of containing the analyte to an application zone positioned at a first end of a layer of a porous medium. The sample is allowed to travel through a plurality of binding zones and a capillary channel, each binding zone comprising a concentration of immobilized binding reagent and the capillary channel comprising fluid barriers in the porous medium. The method also involves detecting a number of binding zones that have undergone a binding event between the binding reagent and the analyte. The method further comprises determining an amount of analyte based on the number of binding zones that have undergone a binding event.
Another aspect of the present invention provides a method for making an immunoassay device comprising providing a layer comprising a continuous porous medium deposited thereon and etching the medium to provide fluid barriers in the porous medium. At least a portion of the barriers define a capillary channel. The method further comprises depositing a plurality of binding zones within the fluid barriers, each binding zone being defined by a concentration of binding reagent immobilized on the medium.
Another aspect of the present invention provides a device for facilitating removal of fluids, comprising a fluid pathway defined within a layer of a porous medium. The device also comprises a reservoir positioned at a terminal end of the pathway, the reservoir comprising a series of capillary channels inscribed in the porous medium. Each of the channels are adjacent at least one other channel and each capillary channel is contiguous with the fluid pathway.